It reads to me like just an annoyance you can get rid of.
Yep. It says it's more of an annoyance, but if you try to load XML in Firefox that has leading white spaces, it is render breaking. (Though there is a possibility that it's my suite of design and dev tools that are actually breaking it - it may not break on a naked Firefox install).
Leading white space is an issue in a lot of different parsing and output generation routines. I can't even begin to count the hours I wasted the first time I put myself in that situation. Now, it's one of the first things I check when an application that I'm working on is tossing a parse our output error. Trailing space can be an issue too - though it doesn't usually prevent things from running, it can affect system memory since the stream never gets properly closed and thus it hangs in memory until much later than it should.
Anyway - glad we locked in on this. Hopefully it will save devdev some hair pulling.